Auger-type pilot bit

ABSTRACT

Following is disclosed a drill bit especially adapted for use as a pilot bit in drilling foundation holes and which has a substantially conical body. Two blade portions, spaced 180* apart, extend from the body in spiral fashion from a common joining region adjacent the apex of the body. Each blade has a concave leading surface of small radius in transverse cross section and a trailing surface of larger radius than that of the body. The blades terminate beyond the apex of the body, being connected with a substantially horizontal line tangential with their cutting edges. Further, a connection means is disclosed having a depression in the base of the body, with a first region having in transverse cross section two opposite, parallel sides connected at each end with a curved surface substantially parallel with the exterior surface of the body. A second region extends from the first region toward the apex of the body and is substantially rectangular in transverse cross section with its end region facing the blades. A male connection member registers with said depressions and is secured therein by a fastener which extends through the bit body.

United States aet [72] Inventor John V. Watson Fort Worth, Tex. [21] Appl. No. 668,915 [22] Filed Sept. 19, 1967 Patented Jan. 26, 1971 [73] Assignee Watson Manufacturing Company Fort Worth, Tex.

[54] AUGER-TYPE PILOT BIT 3 Claims, 10 Drawing Figs.

[52] US. Cl 175/421 [51] E2lb 9/06 Field of Search 175/392, 421, 395

[56] References Cited UNITED STATES PATENTS 1,848,192 3/1932 Newman l/421X 2,289,707 7/1942 Hellman /421X 2,639,122 5/1953 Petersen..... 175/392 2,773,673 12/1956 Petersen..... 175/392 2,870,995 l/l959 Petersen..... 175/392 2,877,987 3/1959 Petersen..... 175/392X 3,016,117 l/1962 Petersen..... 175/392X 51,051 11/1865 Houghton 175/395 Primary Examiner-Nile C. Byers, Jr. Attorney-Wofford and Felsman ABSTRACT: Following is disclosed a drill bit especially adapted for use as a pilot bit in drilling foundation holes and which has a substantially conical body. Two blade portions, spaced apart, extend from the body in spiral fashion from a common joining region adjacent the apex of the body. Each blade has a concave leading surface of small radius in transverse cross section and a trailing surface of larger radius than that of the body. The blades terminate beyond the apex of the body, being connected with a substantially horizontal line tangential with their cutting edges. Further, a connection means is disclosed having a depression in the base of the body, with a first region having in transverse cross section two opposite, parallel sides connected at each end with a curved surface substantially parallel with the exterior surface of the body. A second region extends from the first region toward the apex of the body and is substantially rectangular in transverse cross section with its end region facing the blades. A male connection member registers with said depressions and is secured therein by a fastener which extends through the bit body.

AUGER-TYPE PILOT BIT BACKGROUND AND GENERAL DISCUSSION Previously known pilot bits include those disclosed by Petersen in his US. Pat. Nos. 2,578,014; 2,639,122; and 2,773,673. Significant widespread commercial success has followed these advances in the art, particularly with pilot bits of the type disclosed in US. Pat. No. 2,773,673. Such bits perform advantageously over previously known bits but nonetheless have a number of significant deficiencies, not the least of which flows from the utilization of fishtail leaders which extend beyond the apex of the conical body. Frequently, these leaders fracture, especially when drilling harder formations, leaving the bit without structure suitable for removing the earths formation from the center of the borehole bottom. And yet, it is essential that suitable structure be provided for disintegrating the center of the borehole bottom, and consequently, I sought means to perform this function with efficiency but with decreased tendency of structural failure. Accordingly, I originated at cutting blade configuration which utilitizes two blade portions spaced l80 apart that spiral upward and outward from a region adjacent the apex of a conical body, with said region terminating beyond the apex of the body on the centerline thereof and with the cutting edges being connected with a substantially horizontal line, tangential as seen in plan view with the curved portion of the cutting edges. Superior blade strength is achieved through utilization of a leading surface which extends between the cutting edge of the blade and the bit body with a radius smaller as seen in transverse cross section than the radius of the body. Moreover, the trailing edge of each blade has a larger radius in transverse cross section than the radius of the bit body and is tangential therewith.

The above configuration enables the provision of improved means for connecting the pilot bit to the parent drill bit. The pilot bit body has a depression which includes a first region which has, in transverse cross section, two opposite parallel sides connected at each end with a curved surface substantially parallel with the exterior surface of the body and its associated blade portion. A second region of the depression extends toward the apex of the conical body from the first region and has a substantially rectangular form in transverse cross section with its end regions facing the blade portions. A male connection member which may be connected with the parent bit has first and second regions that mate with the first and second regions of the depression in said body. The second region of the male connection members has an elongated aperture that registers with a generally circular aperture extending transversely through the body. The above-described connection means utilizes to an essentially maximum degree the space provided by the exterior configuration of the pilot bit and transmits forces therebetween with minimum likelihood of structural failure.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevation view of a pilot bit embodying the principles of my invention;

FIG. 2 is an exploded front elevation view of the pilot bit of FIG. 1 and its male connection means;

FIG. 3 is a side elevation of the pilot bit of FIG. 1 as seen rotated approximately 30 about its longitudinal axis;

FIG. 4 is a plan view as seen from the bottom of the bit os FIG. 1;

FIG. 5 is a fragmentary side elevational view as seen looking at 90 from the right side of the bit as shown in FIG. 3;

FIG. 6 is a plan view as seen from the top of the bit shown in FIG. 1;

FIG. 7 is a cross-sectional view as seen looking along the lines VII-VII of FIG. 1;

FIG. 8 is a plan view of a male connection means utilized to connect the bit to a parent bit or the like;

FIG. 9 is a front elevation view of the male connection member shown in FIG. 8; and

FIG. 10 is an exploded side elevation view of the male connection member and drill bit shown in FIG. 2 but rotated DESCRIPTION OF A PREFERRED EMBODIMENT The numeral 11 in the drawing designates the body of a pilot bit which is substantially conical, but somewhat ellipsoidal or ogive in longitudinal section, as perhaps best seen in FIG. 2. It is substantially circular in each transverse cross section as may be best seen in FIG. 4. Beginning at the base 13 of the conical body, two spiraled blades 15, 17 are spaced substantially apart and extend in spiralled, auger fashion toward a common joining region A at the rounded apex 19 of the body. These blades each have identical concave leading surfaces 21 defined in transverse cross section by a radius that is small relative to the radius that defines the conical body at that section. As may be seen in FIG. 4, the radius of leading surface 21 at the base of the bit is less than one-quarter as large as the radius of the conical body. Similarly, the radius at transverse section VII-VII is less than a quarter as large as the radius of the bit body. This general relationship between the two above-mentioned radii continues until the apex of the conical body is reached, at which region radius 21 becomes relatively larger owing primarily to the continued spiralled configuration of the blades over the apex of the conical body.

Each spiralled blade has a convex trailing surface 23 (see FIG. 4) defined in transverse cross section by a radius that may be approximately one-third larger than the radius used to define the conical body in that section, thereby increasing from the apex toward the base of the bit. This radius extends from the cutting edge of each cutting blade into tangential communication with the bit body.

The blades 15, I7 terminate beyond the apex of the conical body on its centerline with the cutting edge of the blades l5, 17 being connected with a substantially horizontal straight line region A that is tangential with the spiralled cutting edges of each blade. Region A may be curved somewhat in the form of an ogive if it does not become too pointed and therefore weakened.

Connection means used to secure the bit to a parent bit or equivalent comprises a depression extending toward the apex from the base 13 of the conical body. This depression consists of two regions, the first of which is designated by the numeral 25 and includes curved surfaces 31 and 33, each of which is substantially parallel with an exterior surface of the bit and a tangential trailing edge 23 of the blade. Surfaces 31, 33 extend into communication with parallel sides 39, 41 which extend to a horizontal surface 43. Parallel surfaces 39, 41 are preferably disposed at a slight angle (7% or example) with the straightline region B (see FIG. 4) on the exterior of the bit.

A second region is rectangular in transverse cross section, being defined by elongated sides 45 which intersect the short sides 47. This region extends toward the apex of the conical body from the first region with the short sides 47 facing the blades 15, 17. An aperture 49, preferably countersunk as indicated by the numeral 51, is disposed at generally 90 with the elongated sides 45 of the second region of the bit body and extends therethrough.

As indicated in FIGS. 2 and 3, a male connection member 53, which depends from a portion 55 of the parent bit or equivalent, has first and second regions that mate with the first and second regions of the depression of the body. That is, the geometric configuration of the first region 57 of the connection member mates with the surfaces of the first region of the depression and similarly, the geometric configuration of the second region 59 of the connection member mates with the configuration of the surfaces of the second region of the depression of the bit body. The second region 59 of the connection member has an elongated aperture 61 which registers with the aperture 49 of the bit body such that a fastener such as indicated by the numeral 63 in FIG. 10 may be inserted therethrough to secure the body to the connection member.

It should be apparent from the foregoing that I have provided an invention having significant advantages. The

geometry of the bit body and blades produces a degree of ruggedness which effectively prevents failure of any component except at the expiration of the natural life of the bit. The increase in the radius which defines the leading surface in each cross section from the apex toward the base of the bit enables cuttings to travel upward more easily. The configuration of the blades in their joining region at the apex of the conical body withstands the severe forces generated in this area through contact with the center of the borehole bottom. Simultaneously, fast penetration rates are maintained owing to this configuration. Moreover, the configuration of the blades and bit body at the base and intermediate regions thereof enables utilization of a depression and mating connection member of unique geometric forms which cooperate to fully utilize the space available in the bit body to effectively transmit forces between the connection member and bit body in a manner to minimize failures. This result is achieved by positioning driving shoulder X (see FIG. 4) behind the forces transmitted through cutting edge Y, which causes the structures in zone Z to be subjected to compressive forces but not bending moments.

While I have shown my invention in only one of its forms it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes and modifications without departing from the spirit thereof.

lclaim:

l. A pilot bit comprising:

a substantially conical body having a substantially circular form in transverse cross section;

two spiralled blade portions on said body spaced substantially 180 apart and extending from a common joining region at the apex of said body and extending upward to define augerlike cutting edges with a concave leading surface having a radius about one-quarter the size of the radius of the conical bit body at their common transverse cross sections, and with a convex trailing surface having about a one-third larger radius than the radius of said body at said section;

said blade portion terminating beyond the apex of said conical body on the centerline of said body, with the cutting edges being connected with a substantially horizontal straight line portion tangential sa as seen in plan view with said spiralled cutting edges; and

connection means formed on said body for securing said bit to a drilling element for rotation of said bit.

2. The pilot bit defined by claim 1 wherein a depression is formed in said body to extend from its base toward its apex, said depression comprising:

a first region having in transverse cross section two opposite, parallel sides connected at each end with a curved surface substantially parallel with the exterior surface of the body and blade portion and defining a driving shoulder behind the forces transmitted through each blade edge; and 4 a second region extending toward the apex of said conical body from said first region, said second region being substantially rectangular in form in transverse cross section with its and regions facing said blade portions.

3. In combination with the pilot bit defined by claim 2, a male connection member having first and second regions that mate with said first and second region of said male connection means having an elongated aperture that registers with a generally circular aperture extending transversely through said body. 

1. A pilot bit comprising: a substantially conical body having a substantially circular form in transverse cross section; two spiralled blade portions on said body spaced substantially 180* apart and extending from a common joining region at the apex of said body and extenDing upward to define augerlike cutting edges with a concave leading surface having a radius about one-quarter the size of the radius of the conical bit body at their common transverse cross sections, and with a convex trailing surface having about a one-third larger radius than the radius of said body at said section; said blade portion terminating beyond the apex of said conical body on the centerline of said body, with the cutting edges being connected with a substantially horizontal straight line portion tangential sa as seen in plan view with said spiralled cutting edges; and connection means formed on said body for securing said bit to a drilling element for rotation of said bit.
 2. The pilot bit defined by claim 1 wherein a depression is formed in said body to extend from its base toward its apex, said depression comprising: a first region having in transverse cross section two opposite, parallel sides connected at each end with a curved surface substantially parallel with the exterior surface of the body and blade portion and defining a driving shoulder behind the forces transmitted through each blade edge; and a second region extending toward the apex of said conical body from said first region, said second region being substantially rectangular in form in transverse cross section with its end regions facing said blade portions.
 3. In combination with the pilot bit defined by claim 2, a male connection member having first and second regions that mate with said first and second region of said male connection means having an elongated aperture that registers with a generally circular aperture extending transversely through said body. 